I am in the middle making a few purchases for my AC kit and was wanting some tips/advice on anything I may not have, or alternative suggestions. I generally work as a 1st AC on low budget Short films, Music videos, TV Drama, and Commercials. I want to build a kit that is flexible between job to job and could be used for indie features.

I like to carry lots of cables. At some point this is an unscratchable itch, but there's no great expense in having a few BNC patch cables, HDMI cables and adaptors, and so on, in the box. Also a variety of audio cables and adaptors, attenuators, and perhaps a small isolation transformer and distribution amplifier. Audio is often the poor relation and it's often only a trivially inexpensive adaptor or cable that prevents people getting a feed to their ipod earbuds. In a similar vein it is becoming increasingly necessary to own converters from HDMI/SDI and vice versa. 4-pin XLR power cables to and from everything in the world. Learn how to build your own.I suspect more regimented shooting regimes on high end productions might make all of these someone else's problem, but it's always nice to be able to pull out something quickly.

What are you doing for power for the monitor? I like the battery systems that are based around the little Sony NP-F series. They're small and handy for slapping on a monitor, and you can get adequately-good third party ones (the Sony types are horrendously expensive, and I've found that the best of the Chinese clones are fine - test first, obviously). You can even get adaptors that take two and put them on an anton/bauer plate for you.

Miniature adjustable spanner (er, wrench, americans). Do not use a leatherman as pliers to handle nuts. It damages the nut.

Sticky velcro, and solvent for removal (careful you don't melt someone's camera, though). Also velcro cable ties, the type that you can make temporarily captive on the cable.

Ratchet straps to attach things to the cart.

Wooden clothes pegs and metal clips. Yes, yes, I know, that's grip and electric's job, but better have one than need to beg.

Very good call on the USB power pack and USB light. I should get that...

If you are doing a lot of digital work, I would add an Arctic Butterfly (non static brush), especially designed for sensor cleaning, a bulb syringe for the same thing and a lit loop magnifier for inspecting the cleanliness of the sensor. Keep your kit simple. Don't overwhelm yourself with crap you won't use or need.

A Leica Disto or Hilti laser rangefinder with a viewfinder is a good investment. They'll run you about $500, but totally worth it. Bright Tangerine soft tape (Rabone replica). Stanley Fatmax 16' hard tape.

Would be good to have your own headset with a comfortable ear mold. Headlamp for wrapping in the dark. Anton Bauer d-tap splitter can be a lifesaver. Gum. Altoids. Tilley Hat for outdoors (SPF50!). Sunscreen. A good knife. Torx keys for Red cameras. Long shaft flathead screwdriver for those silly Zacuto plates. Extra 1/4-20 and 3/8-16 screws. Extra BNC barrels, T's, elbows. Bongo ties.
Standard and metric allen keys. PCam for your iPhone.